Material dispensing assembly

ABSTRACT

A material dispensing assembly ( 100 ) and method of operation for converting a portable cartridge dispensing tool to a bag-type dispensing tool is provided in which the assembly includes a single piece piston ( 110 ) for advancing material though a material housing ( 104 ). The single piece piston ( 110 ) includes a substantially square-shaped receptacle ( 140 ). The assembly further includes a square shaped drive rack ( 112 ) for attaching to the piston ( 110 ) at the substantially square-shaped receptacle ( 140 ) at a connection end ( 128 ). The drive rack ( 112 ) further includes a plurality of teeth ( 142 ) located thereon. The assembly ( 100 ) further has a support ( 127 ) with a substantially square profile for receiving and supporting the drive rack ( 112 ) during operation such that the construct of the drive rack and piston ( 110 ) are prevented from rotating during operation.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application filed under 35.U.S.C. §120 claiming priority to U.S. patent application Ser. No.13/857,235 and publication number U.S. 2013-0306670 published Nov. 21,2013 that was filed on Apr. 5, 2013 now U.S. Pat. No. 8,950,627 thatissued on Feb. 10, 2015, which is a divisional application of U.S.patent application Ser. No. 12/434,024 filed on May 1, 2009 now U.S.Pat. No. 8,424,727 that issued on Apr. 23, 2013, which claims priorityto U.S. Provisional Application Ser. No. 61/050,406 that was filed onMay 5, 2008 and entitled MATERIAL DISPENSING ASSEMBLY. This continuationapplication claims priority to the above-identified patent applicationsand patents and incorporates the above-identified applications andpatents herein by reference in their entireties for all purposes.

TECHNICAL FIELD

The present disclosure relates to a material dispensing assembly, andmore particularly, a material dispensing assembly for sausage orbag-type dispensing tools.

BACKGROUND

Dispensing tools have been available for a number of years, assisting inthe application of material to a desired surface in residential,commercial, or manufacturing environments. Such materials include, forexample, adhesives, lubricants, and sealants such as, silicone,urethanes, and caulk. Conventional dispensing tools frequentlyvisualized are of the type of a handheld caulk gun 10, as illustrated inFIG. 1. Cartridges 12 shown in FIG. 2 having any number of differenttypes of materials, including those listed above are inserted into acartridge support sleeve 14 located on the top side of the dispensingtool 10. A trigger 16 on the gun 10 when actuated drives a rack 18having a plunger 20 that engages the material located in the cartridge12 such that each actuation of the trigger, forces material to bedispensed from a nozzle 22 located at an end 24 of the cartridge.

A more modern dispensing tool for applying various materials, includingthose materials listed above is a power dispensing gun 30, having abattery, pneumatic, or other means for powering motor for portable useis illustrated in FIG. 3. The power dispensing gun 30 is also capable ofusing the cartridges 12 filled with dispensing material by inserting thecartridges 12 into a support sleeve 32 located on the top of the powerdispensing gun 30. A trigger 34 on the power dispensing gun 30 isactuated, driving a rack 36 having a plunger 38 that engages thematerial located in the cartridge 12 such that each actuation of thetrigger forces material to be dispensed from a nozzle 40 located at theend 42 of the gun. Further details of the operation and configuration ofa power dispensing gun is explained in U.S. patent application Ser. No.11/918,689 entitled POWERED DISPENSING TOOL AND METHOD FOR CONTROLLINGSAME that is assigned to the assignee of the present invention and isincorporated herein by reference in its entirety for all purposes.

Cartridges 12 are not the only form of container for holding materialused by the dispensing guns 10, 30, but another known type of containeris a sausage pack or bag-type container 50 shown in FIG. 4. The sausagepack 50 includes a first and second ends 52, 54, respectively extendingfrom a main body 56 having dispensing material therein. The sausage pack50 is positioned in a housing tube 58 located on the guns 10, 30 inplace of the cartridge support sleeves 14, 32, respectively asillustrated in FIGS. 5 and 7. The sausage pack 50 once inserted into theguns has an opening 60 (shown in phantom is typically formed fromremoval of a containment ring or by piercing the sausage pack) towardthe nozzle 22, 40 and the plunger 20, 38 squeezes the material out thenozzle when the trigger 16, 34 is engaged.

One example of a dispensing tool having interchanging support sleevesincludes U.S. patent application Ser. No. 11/973,242 filed on Oct. 5,2007 entitled DISPENSING TOOL that is assigned to the assignee of thepresent invention and is incorporated herein by reference in itsentirety for all purposes. The '242 application illustrates a system forinterchanging support sleeves from a cartridge-type dispenser to asausage pack dispenser and vice versa as desired by the operator on asingle power dispenser.

Sausage packs 50 are typically more economical because of their cheaperfabrication. As a result, the sausage packs 50 are typically used morefrequently in high volume commercial and manufacturing operations overconventional cartridges 12 in material dispensing guns.

SUMMARY

One example embodiment of the present disclosure includes a materialdispensing assembly for converting a portable cartridge dispensing toolto a bag-type dispensing tool. The assembly comprises a single piecepiston for advancing material though a material housing. The singlepiece piston includes a substantially square-shaped receptacle. Theassembly further comprises a square shaped drive rack for attaching tothe piston at the substantially square-shaped receptacle at a connectionend. The drive rack further comprises a plurality of teeth locatedthereon. The assembly further has a support with a substantially squareprofile for receiving and supporting the drive rack during operationsuch that the construct of the drive rack and piston are prevented fromrotating during operation.

Another example embodiment of the present disclosure includes asingle-piece piston for advancing material in a dispensing gun. Thepiston comprises first and second ends, the first end having a domeprofile with an annular taper extending outwardly toward the second end.The piston further comprises a circular seal lip integral with andextending about the perimeter of the piston, the circular seal lipincludes a plurality of substantially equal segments locatedtherebetween. A noncircular attachment aperture is located in the pistonfor attaching the piston to a dispensing gun. The noncircular attachmentaperture in the piston prevents loosening and rotation of the pistonduring operation.

A further example embodiment of the present disclosure includes amaterial dispensing gun assembly comprising a single piece piston foradvancing material though a material housing. The single piece pistonincludes a substantially square-shaped receptacle for attaching thesingle piece piston to a dispensing gun and first and second ends. Thefirst end includes an annular dome profile with first and second annulartapered surfaces extending outwardly toward the second end. The pistonfurther comprises a circular seal lip integral and extending from thesecond annular tapered surface about the perimeter of the piston, thecircular seal lip further comprises a plurality of substantially equalsegments. The dispensing gun assembly also comprises a square shapeddrive rack for attaching to the single-piece piston at the substantiallysquare-shaped receptacle at a connection end and a plurality of teethlocated thereon. The dispensing gun also includes a support having asubstantially square profile for receiving and supporting the drive rackduring operation such that the construct of the drive rack and pistonare prevented from rotating during operation.

A yet further example embodiment of the present disclosure includes amethod of dispensing material from a material dispensing gun comprisingloading a sausage bag comprising dispensing material into a tuberemovably attached to a dispensing gun, the tube having an exit end fromwhich the dispensing material is dispensed during operation. The methodalso comprises locating the sausage bag between the exit end and asingle piece piston in the tube and engaging the sausage bag with anannular dome located at a front end of the single piece piston locatedin the tube. The method further comprises advancing the single piecepiston against the sausage bag with a rack fixedly attached to thesingle piece piston such that material located in the sausage bagengaged by the annular dome is dispensed from the exit end of the tubeand unadvanced material not engaged by the annular dome extends overfirst and second tapered annular surfaces of the dome. The method alsoincludes engaging the unadvanced material in the sausage bag with acircular seal lip integral and extending from the second annular taperedsurface about the perimeter of the piston, the circular seal lipcomprises a plurality of substantially equal segments located about theperimeter of the circular seal lip and advancing the unadvanced materialwith the plurality of substantially equal segments of the single piecepiston such that the unadvanced material located in the sausage bagengaged by the plurality of segments is dispensed from the exit end ofthe tube.

Another example embodiment of the present disclosure includes a materialdispensing housing for use with bag-type dispensing material. Thematerial dispensing housing comprises a transparent tube for supportingbag-type dispensing material, the tube is formed from high-temperatureresistant polymeric material. The transparent tube allows for thevisualization of the movement of dispensing material located within thehousing during operation. The housing also comprises a base coatingselected from one of a silicone coating and polysiloxane coating. Thebase coating provides superior service life and reduced friction of thebag holding the dispensing material and reduces the friction with apiston that engages the tube and the bag-type dispensing material duringoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present inventionwill become apparent to one skilled in the art to which the presentinvention relates upon consideration of the following description of theinvention with reference to the accompanying drawings, wherein likereference numerals refer to like parts throughout the drawings and inwhich:

FIG. 1 is a side elevation view of a manual dispensing gun adapted for acartridge-type material container;

FIG. 2 is a side cross sectional elevation view of a cartridge-typematerial container for use in a manual or powered dispensing gun;

FIG. 3 is a side elevation view of a power dispensing gun adapted for acartridge-type material container;

FIG. 4 is a side elevation view of a sausage pack material container foruse in a manual or powered dispensing gun;

FIG. 5 is a perspective view of a tube for housing a sausage packmaterial container of FIG. 4;

FIG. 6 is an exploded assembly view of a material dispensing assemblyadapted for a power dispensing tool constructed in accordance with oneembodiment of the present disclosure;

FIG. 7 is a side view of a power dispensing gun adapted to support thematerial dispensing assembly of FIG. 6;

FIG. 8A is a rear isometric view of a single piece piston constructed inaccordance with one embodiment of the present disclosure;

FIG. 8B is a front isometric view of the single piece piston constructedin accordance with the example embodiment of FIG. 8A;

FIG. 8C is a rear elevation view of the single piece piston constructedin accordance with the example embodiment of FIG. 8A;

FIG. 8D is a side elevation view of the single piece piston constructedin accordance with the example embodiment of FIG. 8A;

FIG. 8E is a front elevation view of the single piece piston constructedin accordance with the example embodiment of FIG. 8A;

FIG. 8F is a cross-section elevation side view of the single piecepiston constructed in accordance with the example embodiment of FIG. 8A;and

FIG. 8G is a magnified view of a portion of the single piece pistoncross-section identified in the example embodiment of FIG. 8G.

DETAILED DESCRIPTION

The present disclosure relates to a material dispensing assembly 100,and more particularly, a material dispensing assembly for easilyconverting portable cartridge dispensing tools to sausage or bag-typedispensing tools. One example embodiment of the material dispensingassembly 100 is illustrated in FIG. 6. The assembly 100 can be adaptedto convert a power dispensing tool from the cartridge-type dispenserillustrated in FIG. 3 to that of a sausage type dispenser as illustratedin the example embodiment of the power dispensing tool 102 in FIG. 7that can be powered by battery, pneumatic means, and the like.

The power dispensing assembly 100 of FIG. 6 comprises a sausage holdingtube 104 having first and second ends 106, 105, respectively. A sausagepack 50 of various lengths is installed through the first end 106 andmaterial within the sausage pack is forced out by a piston 110 that islocated behind the sausage pack in the second end 108 during operation.The material that is dispensed from the sausage pack 50 could includecaulk, adhesives, silicone, urethanes, and the like without departingfrom the spirit and scope of the claimed invention. The piston 110 isadvanced by a square piston rack 112, which forces the piston againstthe sausage pack 50, forcing material to dispense from the first end 106through a nozzle 114 that is retained to the tube 104 by a cap 116 via athreaded connection 117.

The amount and speed of the material dispensed from the sausage pack 50by the piston 110 could be a function of the speed of the motor(internal to the gun), or the extent of travel by the piston in the tube104. For example, the piston 110 could “bottom-out” against an emptysausage pack 50 that is compressed against the cap 116 and nozzle 114.The rack 112 moveably passes through components internal to the gun 102,including a pinion gear 118 (that engages and drives the rack in bothforward and reverse directions) coupled to a gear set 120 driven in botha forward and reverse direction by a motor 122. The positioning of thegear set 120 and pinion gear 118 in combination with supports 124internal to the gun 102, fix the orientation of the rack 112 through itspath of travel when advancing and reversing the piston 110 in the tube104. The supports 124 comprise square shaped bushings, guides, orfixtures that maintain the orientation of the rack 112 to preventrotation of the rack or piston 110 during operation.

The rack 112 includes first 126 and second 128 ends. The first end 126passes through a barrel screw 127, spacer 130, end cap 132, and washer134. The barrel screw 127 couples the dispensing assembly 100 throughthe spacer 130 and end cap 132 to mating threaded connection 133 locatedin a housing porting 135 of the gun 102 for engagement with the barrelscrew. Attached to the first end 126 of the rack 112 is a rack handle136 for assisting in the reloading and unloading of the sausage packs 50from the tube 104. The rack handle 136 is secured to a threaded aperturelocated in the first end 126 of rack by a screw 138.

The first and second ends 106, and 108, respectively have respectivethreaded sections 106A and 108A. The first threaded section 106A co-actswith internal threads 116A associated with cap 116 and secures the capto the first end 106 of the tube 104, looking the nozzle 114 between thetube and cap at the first end. The second threaded section 108A co-actswith internal threads 132A associated with end cap 132. Once the end cap132 is secured to the housing 135 of the dispensing gun 102, asdescribed above, the second threaded second 108A is screwed into the endcap, thereby supporting the tube 104 to the housing.

Plungers 20 used in conventional dispensing guns (see FIG. 1), arecommonly threaded on the end of a drive rack 18. Tightening the plunger20 to the rack and applying a lock-nut is a typical means of securingthe plunger. As some cartridges 12 and their corresponding supportsleeves are designed to be rotated, the tendency to have the plunger 20“unscrew” from the drive rack is appreciable, especially duringoperations when the user is attempting to turn the cartridge 12 whilethere is axial pressure being applied to the drive rack.

Such problems are resolved by one embodiment of the present invention.In particular, the rack 112 comprises a square configuration to bereceived and attached to a corresponding a square receptacle 140 in thepiston 110, as illustrated in FIGS. 8A, 8C, and 8F. The rack 112 engagesthe receptacle until it is in contact with an internal face 141 in thepiston 110 and is secured to the piston by a fastener 143 that passesthrough an opening 165 into a counter-bore 167, for seating the fastenerduring attachment. Such design and the corresponding square supports 124internal to the gun 102 prevent rotation of the rack 112 and precludeany loosening of the piston 110.

The rack 112 construction in the illustrated embodiment of FIG. 6provides yet another advantage from the present disclosure. The squarepiston 110, corresponding square receptacle 140, and rack 112 allow therack to be reversed such that the first end 126 can be flipped with thesecond end 128. This reversible rack 112 feature is advantageous whenthe rack becomes worn by the pinion gear 118 along an advanced direction(see arrow A in FIG. 6). At such time that the rack 112 shows signs ofwear, the mirror image construction and corresponding attachments allowthe rack to be flipped 180 degrees between the first and second ends126, 128 while remaining in the same orientation as shown in FIG. 6. Thepinion 118 now drives unworn teeth 142 in the advanced direction “A”.The fasteners 138, 143 and receiving threaded connections in the rack112 at first and second ends 126, 128 are the same, allowing the piston110 and rack handle 136 to be reversed, extending the life of the rackas discussed above.

The piston 110 provides several advantages illustrated in the exemplaryembodiment of FIGS. 6 and 8. While conventional plungers 20 aretypically configured from multiple pieces, the piston 110 is a singleuniform piece made from a single molding operation. This eliminates bothmaterial and assembly costs experienced in conventional plunger designs.While the piston 110 can be made from any number of suitable polymericmaterials, the construct of the piston in the example embodiment isformed from Nylon 66 material. The polymeric material of the piston 110advantageously weighs less than one ounce, while compared toconventional plungers that weigh much more and up to eight ounces. Thereduction in weight in the exemplary embodiment of the single piecepiston 110 reduces stress, strain, and other ergonomic issues typicallyexperienced in wrists and arms of operators using conventionaldispensing guns.

The piston 110 comprises front 144 and back 146 ends as shown in FIGS.8B and 8D, an annular dome 148, and circular lip portion 150, as shownin FIG. 8C. The construct of the annular dome 148 at the front 144 ofthe piston 110 is designed to extrude the maximum amount of materialfrom the tube 104 and sausage packet 50 therein. In particular, the dome148 comprises a first tapered annular surface 151, raising theunadvanced material in the sausage packet 50 up over the tapered annularface to a plurality of segmented sections 152 integrated into the domeand extending from the single piece piston 110. In the illustratedembodiment, twelve (12) segmented sections represented by 152A-152L (seeFIG. 8E) in the circular lip portion 150 capture and advance forward theremaining material in the sausage packet 50 as the piston 110 advancesthrough the tube 104. While twelve segmented sections 152 are shown inthe illustrated embodiment of FIG. 8, more or less segmented sectionscould be used without departing from the spirit and scope of the claimedinvention.

The independent flexibility achieved by the segmented sections 152A-152Lprovide a heightened ability to facilitate a solid lip seal to a tube104 or cartridge 12 internal wall under varying roundness tolerancesespecially experienced in cartridge tubes. Further the specific piston110 diameter, piston lip geometry, including thickness, taper, and edgeangles provide dispensing free of “bag wrap” failures, while enabling alow “pull back” force in sausage-type applications. In addition, thepiston 110 design provides a low drag force in the forward direction(see arrow A in FIG. 6), enabling greater dispensing forces to beachieved. In the illustrated embodiment of FIGS. 8A-8G, the lipthickness represented by dimension “A” in FIG. 8G is approximately 0.34inches, having a front taper 162 of approximately 6 degrees representedby dimension “B”, and edge angle off a rear edge 160 of each segmentedsections 152 of approximately 15 degrees represented by dimension “C”,and a back angle off a second tapered annular surface 163 on the dome151 of approximately 92 degrees represented by dimension “D”, asillustrated in FIGS. 8F and 8G.

The twelve segmented sections 152A-152L are capable under the currentembodiment of FIG. 8 of independently undulating to maintainsubstantially constant regulated pressure to the sausage pack 50,preventing bag wrap failures where the bag of the sausage pack 50 wouldpinch between the plunger and tube in conventional plunger designs. Inthe exemplary embodiment of FIGS. 8A-8G, a vent spacing 154 is providedbetween the 12 segmented sections 152A-152L of approximately 0.030inches represented by dimension “X” in FIG. 8E. The overall length ofthe piston is approximately 1 inch represented by dimension “E” in FIG.8D and the overall diameter of the piston 110 in the illustratedembodiment of FIG. 8 is approximately 2.0 inches as illustrated in FIG.8E by dimension “F”, and the segmented sections extend from the dome 151outward at approximately 0.69 inch diameter radius from the center “O”of the piston. It should be appreciated however, that proportionallylarger and smaller dimensions would be required for larger and smallerdiameter tubes and are intended to be covered by the spirit and scope ofthe claimed invention.

The vent spacings 154 in addition to providing independent pressure tothe inner diameter of the tube 104 and/or sausage pack 50, allow air toescape from the tube when the sausage pack is being inserted or removed.This allows for easier replacement and removal of sausage packs 50during operation by the user. The piston 110 also comprises a number ofvoids on the back end 146. The voids 155 improve the overall structuralstrength and facilitate a reduction in the weight of the piston 110.

The tube 104 in one exemplary embodiment is transparent so that thematerial dispensed from the sausage pack 50 can be observed and visuallymeasured by the user. In addition, the transparent tube 104 allows theuser to visually inspect the tube while performing a cleaning operation.

In another example embodiment, the tube 104 is transparent (i.e., clearand chemical resistant) and made from an a high temperature annealedpolycarbonate or polyimide based material 82 and lined with a basedcoating 84, allowing superior service life in a demanding environment ofrepeated stress, thermal, and chemical attack. Examples of suitable basecoatings include silicone or polysiloxane. Such construction alsoreduces friction with the piston 110 and sausage bag 50 and reduces theforce necessary for dispensing the material from the dispensing gun 102.The base coatings 84 can be applied to the tube 104 by directapplication, such as spraying or wiping the internal portions of thetube, through a heat treatment application process, or by extruding orimpregnating the base material 82 with the base coating material duringthe forming of the base material.

What have been described above are examples of the present invention. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the presentinvention, but one of ordinary skill in the art will recognize that manyfurther combinations and permutations of the present invention arepossible. For example, while the material dispensing assembly wasillustrated being adapted to a power dispensing gun, it could equally beadapted to a manual dispensing gun without departing from the spirit orscope of the claimed invention. Accordingly, the present invention isintended to embrace all such alterations, modifications, and variationsthat fall within the spirit and scope of the appended claims.

The invention claimed is:
 1. A material dispensing assembly for use withbag-type dispensing material, the material dispensing assemblycomprising: a tube for supporting bag-type dispensing material, the tubebeing formed from a temperature resistant polymeric material, the tubeallowing for the movement of dispensing material located within thehousing during operation; and a low friction base coating between apiston and the tube, wherein low friction is below a friction threshold,wherein the friction threshold comprises the friction created by thepiston engaging the tube absent a coating, the low friction base coatingprovides reduced friction, relative to the friction threshold, of thebag holding the dispensing material and reducing the friction with thepiston that engages the tube and the bag-type dispensing material duringoperation; the piston being a single-piece piston for advancing materialin the tube, the piston having a first and second ends, the first endhaving a dome profile with an annular taper extending outwardly towardsaid second end.
 2. The material dispensing assembly of claim 1 whereinthe piston further comprising a plurality of support voids.
 3. Thematerial dispensing assembly of claim 1 wherein said piston is moldedfrom a polymeric material.
 4. The material dispensing housing of claim 1wherein said tube is made from one of polycarbonate and polyamidematerial.
 5. The material dispensing housing of claim 1 wherein saidtube material comprises one of polycarbonate and polyamide material thatis further treated by an annealing process.
 6. The material dispensinghousing of claim 1 wherein said low friction coating comprises one of asilicone coating and a polysiloxane coating.
 7. The material dispensinghousing of claim 1 wherein said low friction coating is provided on aninterior of said tube.
 8. The material dispensing housing of claim 1wherein said low friction coating is impregnated into the polymericmaterial of said tube.
 9. The material dispensing housing of claim 1wherein said low friction coating is extruded with the polymericmaterial of said tube.
 10. The material dispensing housing of claim 1wherein said low friction coating is sprayed onto the polymeric materialof said tube.
 11. The material dispensing housing of claim 1 whereinsaid tube is transparent to allow for the visualization of the movementof dispensing material located within the housing during operation. 12.The material dispensing housing of claim 1 wherein said tube is formedfrom high-temperature resistant polymeric material.
 13. The materialdispensing housing of claim 1 wherein said piston comprises at least oneof a piston diameter, and a piston lip geometry, the piston lip geometrycomprising at least one of a thickness, a taper, and edge anglecomplementary to the tube to provide failure free dispensing of saidbag-type dispensing material from within said tube.
 14. The materialdispensing housing of claim 1 wherein said piston comprises at least oneof a piston diameter, and a piston lip geometry, the piston lip geometrycomprising at least one of a thickness, a taper, and edge anglecomplementary to the tube to enable a low pull back force of saidbag-type dispensing material positioned within said tube, wherein a lowpull back force is a force below a threshold, wherein the thresholdcomprises a force needed in a piston lacking at least one of a pistondiameter, and a piston lip geometry, the piston lip geometry comprisingat least one of a thickness, a taper, and edge angle complementary tothe tube.
 15. The material dispensing housing of claim 1 wherein saidpiston comprises at least one of a piston diameter, and a piston lipgeometry, the piston lip geometry comprising at least one of athickness, a taper, and edge angle complementary to the tube to providea low drag force in a forward direction as said bag-type dispensingmaterial is advanced through said tube, wherein a low drag force is aforce below a threshold, wherein the threshold comprises a force neededin a piston lacking at least one of a piston diameter, and a piston lipgeometry, the piston lip geometry comprising at least one of athickness, a taper, and edge angle complementary to the tube.
 16. Thematerial dispensing assembly of claim 1 wherein said piston furthercomprises: a circular seal lip integral with and extending from saidannular taper about the perimeter of the piston, the circular seal lipcomprising a plurality of substantially equal segments; and anoncircular attachment aperture for attaching said piston to adispensing gun.
 17. The material dispensing assembly of claim 16 whereinsaid annular taper comprises first and second taper portions, the firsttaper portion originating at said first end and a second taper portionoriginating at an end of the first taper portion and extending to saidcircular seal lip at said second end, the first taper having a greaterincline angle than said second taper.
 18. The material dispensingassembly of claim 16 wherein said plurality of segments forming saidcircular seal lip are formed by a vent spacing between each of saidsegments, said vent spacing providing independent movement between eachof said segments during operation.
 19. The material dispensing housingof claim 16 wherein said piston further comprises a vent area betweeneach of said segments and a front taper extending from an outer portionof said segments toward said first end and tapering toward said secondend near an inner portion of said segments in contact with the secondtapered annular surface.
 20. The material dispensing housing of claim 19where said vent areas are located on the piston to provide pressure tosaid tube and to allow air to escape from said tube responsive to alocation of the piston relative to the tube.